JP2000229272A - Work cleaning method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dry cleaning method and device therefor in which effective cleaning work can be performed and the washing device can be miniaturized even for large optical devices by evaluating its cleaning state during the cleaning work. SOLUTION: This device is provided with an energy beam generator 15 for irradiating a work W with an energy beam B to such an extent that the work W is not damaged to remove foreign matters from a cleaning surface F of the work W, a work table 14 for holding the work W, an X-Y stage 12 for changing the irradiation position of the energy beam B to the work W, a cleaning state evaluating device 17 for evaluating the cleaning state of the washing surface F of the work W based on scattered light from the washing surface F of the work W generated accompanying the irradiation of the work W with the energy beam B, and a control means for controlling the actuation of the energy beam generator 15 and the X-Y stage 12 according to the evaluation of the cleaning state of the cleaning surface F of the work W by the cleaning state evaluating device 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for cleaning a surface of a work to which fine foreign matter adheres, and more particularly to a method for cleaning a lens surface of an optical lens made of a material having a high transmission efficiency to ultraviolet rays. It is suitable.

[0002]

_2. Description of the Related Art Conventionally, an optical element such as a lens formed using a fluoride crystal material such as calcium fluoride (CaF ₂ ) or magnesium fluoride (MgF ₂ ) has an extremely wide range of optical characteristics. Because of their excellent transmittance and low dispersion, they are used for high-precision imaging lenses that require high functions, such as high-grade camera lenses and astronomical telescope objective lenses. Further, since such a fluoride-based crystal material has a high transmittance even for light having a short wavelength such as an excimer laser, application to an optical element used in an ultraviolet region is being studied.

When manufacturing an optical element such as a lens or a prism, a material is processed into a rough shape, and a final optical surface shape and surface roughness are obtained by polishing. In addition, in an optical element such as a lens that transmits light, an antireflection film for improving light transmittance is generally formed on the surface (optical surface), and the final polishing step is completed. Cleaning work on the optical surface of the optical element after the cleaning is extremely important. In particular, in the case of a lens for an excimer laser used in the ultraviolet region, a very high transmittance is required, and the final cleaning of the lens affects the optical performance of the lens.

The foreign matter generated in the process of manufacturing such an optical element is inorganic residues such as abrasives and dust, that is, inorganic particles, and organic residues such as oil and fingerprints. These foreign substances are generated in each processing step of the optical element by covalent bonding, electrostatic force, Van der Waals force, or the like.

Conventionally, when cleaning the optical surface of a high-precision optical element requiring high performance, the optical element is immersed in a cleaning tank in which a cleaning liquid is stored, and ultrasonic waves are applied to the cleaning liquid to provide an optical surface of the optical element. The method by the ultrasonic cleaning method for cleaning the surface was generally used.

When the wavelength of light to be used is in the ultraviolet region, such as in an optical system using an excimer laser,
Foreign matter on the surface of the optical element incorporated in this optical system,
In particular, it is known that the transmittance of light is reduced due to organic residues. In order to remove such organic residues, a so-called WE using a cleaning solution as described above is used.
The T method (hereinafter, referred to as a wet method) is not sufficient, and an energy beam is applied to the surface of the semiconductor substrate as described in JP-A-8-509652, and foreign matter on the surface of the semiconductor substrate is removed. It is effective to apply a DRY method (hereinafter, referred to as a dry method) for evaporating and removing a gas to an optical element.

[0007]

The removal of organic residues and inorganic particles from the surface (optical surface) of a lens used in the ultraviolet region can improve the transmittance of an excimer laser beam or the like and form an antireflection film. This is important for improving the durability of the lens later, and is an important factor that affects the optical performance and durability.

When cleaning an optical element by a wet method,
Since it is necessary to arrange a plurality of washing tanks for each washing liquid such as surfactant, pure water, isopropyl alcohol, etc., it is necessary to secure an installation space for these washing tanks.
In particular, when cleaning a large-sized optical element, the entire cleaning equipment becomes large, and the consumption of a solvent used for drying or the like becomes extremely large. In addition, the wet method cannot sufficiently clean an optical element used in the ultraviolet region.

In this regard, the dry method is effective for cleaning optical elements used in the ultraviolet region, and can be said to be a preferable cleaning method from the viewpoint of environmental protection since no solvent is used.

However, the method disclosed in Japanese Patent Application Laid-Open No. 8-509652 only removes organic residues on the surface of the semiconductor substrate, and is not suitable for optical elements having inorganic particles such as abrasive particles and dust on the surface. On the other hand, since it cannot be confirmed during the cleaning operation whether or not this has been removed, it is necessary to perform cleaning again after the completion of the cleaning operation, resulting in a reduction in the efficiency of the cleaning operation.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a dry method capable of performing an efficient cleaning operation by evaluating the cleaning state during the cleaning operation and making the cleaning equipment compact even for a large optical element. A cleaning method and a cleaning apparatus thereof are provided.

[0012]

According to a first aspect of the present invention, there is provided:
A work cleaning method for irradiating a work with an energy beam that does not damage the work, thereby removing foreign matter from the surface of the work, wherein the work generated by the irradiation of the work with the energy beam is provided. The irradiation of the energy beam to the work is controlled based on the scattered light from the surface of the work.

According to the present invention, when the surface of the work is irradiated with the energy beam, foreign matter on the work surface, for example, organic residue is instantaneously evaporated and vaporized, and the inorganic particles are also evaporated by the vaporization energy accompanying the evaporation of the organic residue. Blown off the surface. At this time, the irradiation of the energy beam to the work surface is controlled based on the scattered light of the energy beam from the work surface, and cleaning is performed over the entire surface of the work.

According to a second aspect of the present invention, there is provided an energy beam generating means for irradiating a work with an energy beam to such an extent that the work is not damaged to remove foreign matter from the surface of the work, and holding the work. A work table, a moving device for changing the irradiation position of the energy beam on the work, and a scattered light from the surface of the work generated along with the irradiation of the energy beam on the work. Cleaning state evaluation means for evaluating the surface cleaning state; and control means for controlling the operation of the energy beam generating means and the moving device in accordance with the evaluation of the cleaning state of the work surface by the cleaning state evaluation means. A work cleaning apparatus characterized in that:

According to the present invention, when the surface of the work held on the work table is irradiated with the energy beam from the energy beam generating means, foreign matter, for example, organic residue on the work surface is instantaneously evaporated and vaporized. The inorganic particles are also blown off from the work surface by the vaporization energy accompanying the evaporation of the residue. At this time, the cleaning state of the work surface is evaluated by the cleaning state evaluation means based on the scattered light of the energy beam applied to the work surface. Then, based on the evaluation by the cleaning state evaluation means, the control means controls the operations of the moving device and the energy beam generation means, respectively.

In this way, the moving device is driven to sequentially shift the irradiation position of the energy beam from the energy beam generating means on the work held on the work table, thereby cleaning the entire surface of the work. Is performed.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a method for cleaning a work according to a first embodiment of the present invention, a maximum irradiation amount of an energy beam to a work is set in advance, and the irradiation of the energy beam to the work is performed within a range not exceeding the maximum irradiation amount. In this case, the maximum irradiation amount of the energy beam may be the maximum energy beam irradiation amount such that the irradiation of the energy beam onto the surface of the work does not cause deterioration of the work. When the intensity of the scattered light is equal to or less than a predetermined value, the irradiation of the energy beam to the workpiece may be stopped. In this case, the work may be an optical element having an optical surface, and the optical surface may be irradiated with an energy beam.

The optical element may be formed of a material having a high transmission efficiency with respect to ultraviolet rays. In this case, the material having a high transmission efficiency with respect to the ultraviolet rays may be any one of quartz, calcium fluoride and magnesium fluoride. Good.

In the apparatus for cleaning a workpiece according to the second aspect of the present invention, the cleaning state evaluation means may detect the amount and size of foreign matter on the surface of the workpiece. In this case, the cleaning state evaluation means may evaluate that the cleaning state of the surface of the work is good when the number and size of the foreign substances on the surface of the work are equal to or less than a predetermined value.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a work cleaning apparatus according to the present invention capable of realizing the work cleaning method according to the present invention is applied to a biconvex lens made of calcium fluoride will be described in detail with reference to FIG. However, the present invention is not limited to such an embodiment, and can be applied to technologies in other fields that include similar problems.

An XY stage 12 is mounted on the base 11, and the XY stage 12 is provided with a horizontal first direction and a horizontal second direction orthogonal to the first direction. The stage can be reciprocated by a stage driving device (not shown). A work table 14 having a work holder 13 is mounted on the XY stage 12, and the work table 14 is driven by a table driving device (not shown) around a vertical axis at a predetermined speed, for example, 10 minutes per minute.
It is rotatable at the rate of rotation. Work holder 13
Is a chuck device that holds the work W on the work table 14 in a predetermined posture such that a surface F of the work W to be cleaned (hereinafter, this is referred to as a cleaning surface) faces upward;
In the present embodiment, the outer peripheral edge, that is, the edge surface is gripped so that the optical axis of the biconvex lens is coaxial with the rotation axis of the work table 14.

Above the work table 14, there is provided an energy beam generator 15 for irradiating an energy beam B vertically downward toward a cleaning surface F of a work W mounted on the work table 14. The energy beam generator 15 has an energy density sufficient to remove foreign substances attached to the cleaning surface F, and at the same time, a material constituting the work W, that is, a crystal structure of calcium fluoride is not damaged. Since it is necessary to adjust the energy density and the irradiation time, a beam spot adjusting device 16 for adjusting the diameter of the energy beam B applied to the cleaning surface F to a constant value is attached.

The energy beam generator 15 in this embodiment is a KrF excimer laser oscillator (trade name: LPX200) manufactured by Lambda Physics, and emits an excimer laser beam having a wavelength of 248 nm as a pulse beam at 200 Hz as an energy beam B. Is what you do. Further, the beam spot adjusting device 16 diffuses the energy beam B so that the energy beam B is always a rectangle of 12 × 23 (mm ² ) on the cleaning surface F.

Above the work table 14, a cleaning state for evaluating the cleaning state of the surface of the work W by receiving the scattered light L from the surface of the work W generated by the irradiation of the energy beam B to the work W. An evaluation device 17 is provided. When inorganic particles are present on the cleaning surface F, when the energy beam B is applied thereto, the scattered light L
Varies depending on the size of the inorganic particles.
The cleaning state evaluation device 17 in the present embodiment utilizes such a relationship between the foreign matter on the cleaning surface F and the intensity of the scattered light L,
By continuously detecting the intensity change of the scattered light L,
The size and amount of the inorganic particles intervening on the cleaning surface F are grasped, and the cleaning state of the cleaning surface F is evaluated based on this. That is, when the intensity of the scattered light L is stabilized at a predetermined value or less, it is evaluated that the foreign matter has been completely removed from the cleaning surface F.

The result of the evaluation by the cleaning state evaluation device 17 is output to a control device (not shown) for controlling the operation of the stage driving device, the table driving device, and the energy beam generating device 15. The operation of the driving device is controlled.

The work W in this embodiment has an outer diameter of 20 mm.
0 mm, the radius of curvature of each of the first and second optical surfaces is 25
This is a 0 mm biconvex lens. Before the cleaning operation, abrasives, oils, dusts, etc. adhering to the optical surface which is the cleaning surface F are wiped in advance.

Next, the work W is fixed on the work table 14 using the work holder 13, and the table driving device and the energy beam generating device 15 are operated to rotate the work table 14 together with the work W at a predetermined speed. The center of the lens is irradiated with an energy beam B of 500 mJ / cm ^2, the stage driving device is operated, and the energy beam B is applied to the workpiece W at a rate of 2 mm / sec with reference to the evaluation result by the cleaning state evaluation device 17. The XY stage 12 was driven so as to relatively move in the radial direction.

When the energy beam B is applied to the cleaning surface F of the work W, the organic residue intervening on the cleaning surface F is instantaneously evaporated and vaporized, and inorganic particles are also generated by the vaporization energy accompanying the evaporation of the organic residue. The cleaning surface F is blown off from the cleaning surface F, and the cleaning surface F of the work W is sequentially cleaned.
This cleaning state is evaluated by the cleaning state evaluation device 17, and if it is determined that the cleaning surface F has not yet been sufficiently cleaned, that is, if the intensity of the scattered light L exceeds a predetermined value, the XY stage The operation of the stage driving device is controlled so that the movement speed of the
The cleaning operation was carried out while confirming that the cleaning condition was good, that is, the intensity of the scattered light L was evaluated to be equal to or less than a predetermined value.

However, if the energy beam B is continuously irradiated on the cleaning surface F of the work W, the cleaning surface F of the work W
Is not only damaged, but also the structure of the work W, especially the crystal structure is destroyed. Therefore, the maximum irradiation amount of the energy beam B to the work W is set in advance, and the work W Is irradiated with the energy beam B.

After cleaning the entire cleaning surface F of the work W in this manner, the work W is removed from the work table 14 and the particles on the surface of the work W are evaluated using a known inorganic particle evaluation device. It was confirmed that the particles were almost completely removed. In addition, in the evaluation using a spectroscope, it was confirmed that the organic film residue was almost completely removed, and that the biconvex lens as the work W reached the original transmittance.

Similarly, the radius of curvature of the optical surface is 280 mm
Then, a plano-concave lens (made of SiO ₂ ) having an outer diameter of 250 mm is polished to prepare a work W in which abrasives, oils and other dusts adhered to the surface have been wiped in advance, which is the same as that of the above-described embodiment. Washed similarly. However, the oscillation frequency of the energy beam B was set to 180 Hz.

In the cleaning of the optical surface of such a concave lens, the inorganic particles and organic film residues are almost completely removed, and the cleaning method according to the present invention is extremely effective as a final cleaning treatment of the optical surface of the optical element. Was confirmed.

[0033]

According to the work cleaning method of the present invention, the irradiation of the energy beam to the work is controlled based on the scattered light from the surface of the work generated by the irradiation of the work with the energy beam. Organic residues and inorganic particles can be easily and efficiently removed from the surface of the work without using any of the above-described methods. Particularly, a favorable result is obtained for cleaning a lens using a fluoride material used in an ultraviolet region. Obtainable.

According to the work cleaning apparatus of the present invention, the cleaning state evaluation means for evaluating the cleaning state of the work surface based on the scattered light from the work surface caused by the irradiation of the work with the energy beam; The energy beam generating means and the control means for controlling the operation of the moving device are provided in accordance with the evaluation of the cleaning state of the work surface by the state evaluation means, so that the cleaning equipment can be made more compact even with a large optical element. In addition, the cleaning state of the optical element surface can be evaluated in real time during the cleaning operation, and the cleaning operation can be managed very efficiently by reliably removing organic residues and inorganic particles. .

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of one embodiment in which a workpiece cleaning apparatus according to the present invention is applied to a large-diameter convex lens made of calcium fluoride.

[Explanation of symbols]

 Reference Signs List 11 base 12 XY stage 13 work holder 14 work table 15 energy beam generator 16 beam spot adjuster 17 cleaning state evaluation device W work F work cleaning surface B energy beam L scattered light

Claims (11)

[Claims] 1. A work cleaning method for irradiating a work with an energy beam to such an extent that the work is not damaged, thereby removing foreign matter from the surface of the work, wherein the work is irradiated with the energy beam. A method of cleaning a work, wherein the irradiation of the energy beam to the work is controlled based on the scattered light generated from the surface of the work. 2. The method according to claim 1, wherein a maximum irradiation amount of the energy beam to the work is set in advance, and irradiation of the energy beam to the work is controlled within a range not exceeding the maximum irradiation amount. 3. The work cleaning method according to 1. 3. The maximum irradiation amount of the energy beam is such that the irradiation of the energy beam onto the surface of the work does not cause deterioration of the work. The method for cleaning a workpiece according to claim 2. 4. The work cleaning method according to claim 1, wherein when the intensity of the scattered light is equal to or lower than a predetermined value, the irradiation of the energy beam to the work is stopped. 5. The method for cleaning a work according to claim 1, wherein the work is an optical element having an optical surface. 6. The method according to claim 5, wherein the optical surface is irradiated with an energy beam. 7. The optical element according to claim 5, wherein the optical element is formed of a material having a high transmission efficiency to ultraviolet rays.
Alternatively, the work cleaning method according to claim 6. 8. The method according to claim 7, wherein the material having a high transmission efficiency with respect to ultraviolet rays is one of quartz, calcium fluoride, and magnesium fluoride. 9. An energy beam generating means for irradiating the work with an energy beam to such an extent that the work is not damaged to remove foreign matter from the surface of the work, a work table holding the work, and the work A moving device for changing an irradiation position of the energy beam with respect to the workpiece; and a cleaning state of the surface of the work based on light scattered from the surface of the work generated along with the irradiation of the energy beam to the work. A work comprising: a cleaning state evaluation means; and a control means for controlling the operation of the energy beam generating means and the moving device in accordance with the evaluation of the cleaning state of the surface of the work by the cleaning state evaluation means. Cleaning equipment. 10. The apparatus according to claim 9, wherein the cleaning state evaluation unit detects the amount and size of foreign matter on the surface of the work. 11. The cleaning state evaluation means evaluates that the cleaning state of the surface of the work is good when the number and size of foreign matters on the surface of the work are equal to or smaller than a predetermined value. The work cleaning device according to claim 10.